A relay device is a device that is located between a base station and a terminal to receive and amplify signals from the base station and the terminal. That is, it refers to a device that receives and amplifies a signal from the base station to transmit the amplified signal to the terminal, and receives and amplifies a signal from the terminal to transmit the amplified signal to the base station. The relay device is installed in the place where a wireless transmission and reception condition between the terminal and the base station is bad, to relay a signal and is mostly installed under or in the building where it is difficult for a signal from the base station to arrive at. The structure of the relay device varies depending on a building structure or the characteristic of a shadow area, and when especially used in the building, a relay device in which several antennas are distributed is used.
The distribution/relay device may match and relay an outdoor base station outside the building or match and use a base station for only the distribution/relay device, according to the capacity of a user connected to the distribution/relay device. In the case of long term evolution (LTE), each building matches and uses a small base station, i.e., femto-cell because the capacity of data occupied by a user is large.
The distribution/relay device is connected to several distributed antennas by using a coaxial cable. The coaxial cable is characterized in that it is possible to transmit a high-frequency signal used in a base station without a change in frequency as it is. However, since installing the coaxial cable inside the building costs high, a distribution/relay device that uses an UTP line, one of LAN cables has been studied.
As an example, Korean Patent Publication No. 2010-0068688 employs a method that includes converting a high-frequency signal received from a base station or communication system by a wired or wireless connection into a digital signal, and transmitting, by a digital signal processing unit, the digital signal to an Ethernet cable by using time division multiplexing. The technique connects a signal distribution device to a plurality of remote signal transmission and reception devices by an UTP line, a cheap communication cable that has been previously installed without installing a separate cable and relates to a relay device that may transmit an existing internet signal and a mobile communication signal through the UTP cable together.
However, when a high-speed wireless transmission standard is employed between a base station and a terminal, the technique also causes degradation to transmission quality if there are different transmission time delays between a signal distribution device and a plurality of remote signal transmission and reception devices. Thus, in order to correct a time delay between the signal distribution device and the plurality of remote signal transmission and reception devices to enable the plurality of remote signal transmission and reception devices to perform transmission and reception together, there is a need for a study on a device that fine-tunes a time delay between the signal distribution device and the plurality of remote signal transmission and reception devices.